1. Field of the Invention
The present invention relates to a radio communication apparatus, method and program for controlling communication in a wireless LAN system, and more particularly to a radio communication apparatus, method and program characterized in the process of assigning a channel.
2. Description of the Related Art
The IEEE802.11 wireless LAN system can use a plurality of frequency bands, each band containing a plurality of channels. A wireless LAN communication apparatus can select one of the channels, and perform communication using it. Some of the frequency bands may be commonly used by another system. For example, the LAN system and a radar system commonly use a frequency band of 5 GHz.
For example, in Europe, the wireless LAN system can use frequency bands of 5.15 to 5.25 GHz, 5.25 to 5.35 GHz, and 5.47 to 5.725 GHz. The channels included in the frequency band of 5.15 to 5.25 GHz are allocated for indoor use, and their transmission power is low. Therefore, there is no possibility of their interference with a radar system, and hence it is not necessary to detect a radar signal when using the band. On the other hand, the channels included in the frequency bands of 5.25 to 5.35 GHz and 5.47 to 5.725 GHz can be used both inside and outside, and their transmission power is high. Accordingly, they may interfere with a radar system, and it is necessary, when using those bands, to check whether or not there is a radar signal. In those bands, the channels in which no radar signals are detected can be used.
Jpn. Pat. Appln. KOKAI Publication No. 2001-285301, for example, has proposed a technique for utilizing the periodicity of radar pulses and using a wireless LAN system only for the period in which radar pulses do not interfere with wireless LAN system signals, thereby avoiding interference therebetween.
However, it violates European Telecommunication Standards Institute (ETSI) European standards (EN) 301 893 v1.2.2 to utilize the periodicity of radar pulses and use a wireless LAN system only for the period in which radar pulses do not interfere with wireless LAN system signals. ETSI EN 301 893 v1.2.2 stipulates that when using a channel included in the frequency bands of 5.25 to 5.35 GHz and 5.47 to 5.725 GHz, a period of 60 seconds or more must be prepared to detect a radar. In other words, when using a channel commonly used with a radar system, the wireless LAN system cannot perform communication for at least 60 seconds after it is turned on.
Furthermore, ETSI EN 301 893 v1.2.2 stipulates that where there is a frequency band containing a radar channel, a radar channel will be checked for the presence of a radar signal. When using the channels, it is necessary to confirm that no radar signals exist in the channels. Further, since the probability of selecting a given channel will be the same for all channels, the channels that do not require the detection of a radar signal cannot always be used. Therefore, even a channel that requires detection of a radar signal must be selected sooner or later, and in this case, a detection period of at least 60 seconds is required.